Demand Side Management (DSM) has attracted a huge interest recently in increasing the operational flexibility of modern power systems. This interest is fueled by the integration of a high amount of intermittent renewable energy resources (RES) in the networks. This study has been performed to analyze and identify the potential of DSM in providing the operational flexibility of power networks in 8 South-East European countries. For that purpose, a survey questionnaire was developed on DSM, which was distributed in late 2017 and responses were collected in January 2018. The questionnaire collected information on existing DSM capacities, the required DSM amount for flexible operation and the future DSM potential in the region. Additional key information was collected about the DSM provision, such as the characteristics, location and network services obtained from these resources, as well as the influential market participants to provide these DSM services in the network. This study will facilitate the cross-border management of RES by increasing the operational flexibility of the transmission network in South-East Europe.